The occurrence of thrombosis at a blood-polymer interface presents major design difficulties in the development of small-diameter artificial vascular grafts. The interaction between blood and an artificial surface results in an adsorbed protein layer which affects the extent of platelet deposition and thrombus formation. The factors that determine the nature of this protein layer are not well-defined. We have determined that both the chemical nature of the surface and the conditions of protein adsorption influence the amount of thrombus formation and rate of embolization. We propose to study surface-protein interactions at the molecular level. Commercially-available and laboratory-synthesized biomaterials which have markedly different chemical surface properties will be used in in vitro and canine ex vivo experiments to study the effect of modifications in chemical properties on protein deposition. In vitro deposition of human or canine fibrinogen, fibronectin, vitronectin, and serum albumin onto these materials will be assessed. These proteins will be adsorbed singly, competitively, and sequentially to examine protein-protein interactions on the surfaces. Conformation of the adsorbed protein will be determined by Fourier Transform Infrared spectroscopy and by enzymatic methods. Orientation and distribution of adsorbed proteins will be assessed by immunological methods. In addition, the canine proteins will be preadsorbed onto the materials and tested in the canine ex vivo shunt to determine the whole-blood response in the absence of anticoagulants. The influence of protein conformation, orientation, and distribution on platelet activation will be examined. Scanning and high voltage electron microscopy will be used to assess morphological and cytoskeletal changes in platelets. Video-enhanced microscopy will be used to measure the granule secretion induced by the protein-surface interaction. These studies will extend the current research on the mechanisms involved in artificial surface-induced thrombogenesis and provide information that will aid in the design of biomaterials.